1. Field of the Invention
The present invention relates to a locking device for use with a key which is inserted into the keyway to thereby either operate a manipulated mechanism to be key-operated or maintain the mechanism in its inoperative state. The invention also relates to the key for use with this locking device.
2. Description of the Related Art
A known locking device mounted in an automotive door or the like is described, for example, in Japanese Patent Application Laid-open No. 8-4387. This locking device has a cylindrical rotor case, a sleeve rotatably housed in the rotor case, a key rotor rotatably mounted in the sleeve and provided with a keyway, a rear rotor rotatably mounted so as to oppose to the key rotor in the axial direction, and a lock lever mounted to be capable of integrally rotating with the rear rotor.
With the aforementioned locking device, if an authentic key is inserted into the keyway, the key rotor and rear rotor are coupled together such that they rotate as a unit. Thus, if the authentic key inserted in the key rotor is rotated, the key rotor, rear rotor, and lock lever rotate together with the authentic key. Manipulating force from the lock lever unlocks the locking mechanism in a vehicular door or the like.
Meanwhile, if a key different in shape with the authentic key or a key substitute such as a screwdriver (hereinafter collectively referred to as inauthentic keys) is inserted into the keyway in the key rotor and forcedly rotated, the key rotor and sleeve rotate together. The key rotor is disconnected from the rear rotor, permitting the key rotor to rotate freely. Consequently, if the inauthentic key inserted in the key rotor is rotated, the key rotor and sleeve rotate together idly but neither the rear rotor nor the lock lever rotates. The manipulating force from the lock lever is not transmitted to the lock mechanism. Hence, the locking mechanism is prevented from being unlocked.
In the above-described locking device, plural disk tumblers are radially movably disposed in the key rotor. If an elongated, plate-shaped key is inserted into the keyway, the disk tumblers are brought into engagement with their respective engagement portions spaced from each other and formed on one (engagement surface) of the surfaces provided at both sides in the thickness direction of the key. At this time, if all the disk tumblers of this locking device engage their respective correct engagement portions and move into their normal positions corresponding to the correct engagement portions (normal position) in the radial direction, the key rotor and rear rotor are coupled together such that they can rotate as a unit. The key rotor will be disconnected from the rear rotor if at least one disk tumbler engages an incorrect engagement portion and is not moved into its correct position radially.
That is, if the authentic key is inserted into the keyway and all the disk tumblers engaging with their respective engagement portions of the authentic key are moved into their normal positions, the locking mechanism can be unlocked by rotating the authentic key. Where an inauthentic key is inserted into the keyway and at least one disk tumbler is not moved into its normal position, even if the inauthentic key is forcedly rotated, the key rotor and sleeve rotate idly. Consequently, the locking mechanism is not unlocked. Furthermore, no excessive force is applied to the various components. Hence, the components are prevented from being damaged.
With the above-described locking device, during unlocking, the key must be rotated against the resistances of the key rotor, rear rotor, and lock lever which are produced when they rotate and also against the operative resistance of the locking mechanism. In consequence, considerably large torque is transmitted from the key to the key rotor. Accordingly, in order to prevent deformation of the key certainly, it is necessary to provide a sufficiently large strength to the key in the key-twisting direction. Therefore, the material of the key used with the above-described locking device is limited to materials showing high strength such as iron and stainless steel. In addition, it is necessary to increase the thickness of the wall of the key sufficiently according to the magnitude of the transmitted torque.
Furthermore, the plural disk tumblers disposed in the key rotor are arranged in the axial direction. When the key is inserted into the keyway, the tumblers come into engagement with engagement portions of the key engagement surface which are spaced from each other in the longitudinal direction. Therefore, to diversify the kinds of keys (i.e., combinations of the engagement portions), it is necessary to increase the number of the disk tumblers and the number of installed engagement portions of the key. If the number of the disk tumblers and the number of installed engagement portions of the key are increased, the total length of the device and the total length of the key are inevitably increased.